220 THE HUMAN BODY. 



Sounds of the Heart. If the ear be placed on the chest 

 of another person over the heart region, two distinguisha- 

 ble sounds will be heard during each round of the heart's 

 work. They are known respectively as the first and second 

 sounds of the heart. The first is of lower pitch and lasts 

 longer than the second and sharper sound ; vocally their 

 character may be tolerably imitated by the syllables lub, dup. 

 The cause of the second sound is the closure, or, as one 

 might say, the "clicking up" of the semilunar valves. 

 The first sound takes place during the ventricular sys- 

 tole, and is probably due to vibrations of the tense ven- 

 tricular wall at that time. In many forms of heart disease 

 these sounds are modified or cloaked by additional sounds 

 which arise when the cardiac orifices are roughened, or nar- 

 rowed, or dilated, or the valves inefficient. A physician 

 often gets important information as to the nature of a heart 

 disease by studying these new or altered sounds. 



Function of the Auricles. The ventricles have to do the 

 work of pumping the blood through the blood-vessels. 

 Accordingly their walls are far thicker and more muscular 

 than those of the auricles; and the left ventricle, which has 

 to force the blood over most of the body, is stouter than the 

 right, which has only to send blood around the compara- 

 tively short pulmonary circuit. The circulation of the 

 blood is, in fact, maintained by the ventricles, and we have 

 to inquire what is the use of the auricles. Not unfre- 



Whatdo we hear on listening over the heart region of a living per- 

 son's chest? What are the sounds called? How does the first differ 

 from the second? What words aive some idea of their character? 

 What is the origin of the second sound? Of the first? What occurs 

 as regards the heart sounds in many forms of heart disease? 



What work have the ventricles to do? How do their walls differ 

 from those of the auricles? Which ventricle has the thicker wall? 

 What part of the heart maintains the blood flow?. 



